1. Field of the Invention
The present invention relates to an optical access network system, particularly to an optical access system for dual service network.
2. Description of the Related Art
Fiber-optic communication is a communication method based on optical signal and fibers which is also a kind of cable communication. Light can be used to carry information after being modulated where it features a superior transmission capacity and a high information security. Since 1980s, the fiber-optic communication system plays a very important role in the digital world. In principle, the outgoing information is transferred from the sender side to the transmitter, and the signal modulates the carrier wave, which functions as the transmission medium of information, and then the modulated carrier wave is sent to the recipient side in a distant place, and the receiver demodulates the modulated carrier wave to obtain the original information.
Since the development for wireless and cable network has grown rapidly for the past few years, the demand for higher transmission speed and bandwidth has also increased. Current, the best solution would be to use optical fiber as a transmission carrier between wireless and cable network. As a result, many dual-service optical communication related inventions have been proposed lately, however, those newly proposed inventions still have many obstacles to overcome with. For example, in U.S. Pat. No. 7,127,176, the proposed invention utilizes optical fiber as radio frequency (RF) and uses semiconductor optical amplifier and electro-absorption electro-optic modulator at its base station. However, optical fiber dispersion will decrease signal strength for RF over long distance, create a restriction on its practical applications. Additionally, in the paper “Optical Fiber Communication Conference” released by GK. Chang on 2006, in order to solve the optical fiber dispersion issue among long distance transmission, Chang proposed using Double Sideband Suppressed Carrier Modulation. Unfortunately, this kind of modulation method can only transmit amplitude shift modulation signal, it also required at least two electro-optic modulators which will greatly increase manufacturing cost. To overcome the abovementioned problem, the present invention proposes an optical access system for dual service network which can effectively overcome the problem of RF signal strength being reduced by optical-fiber dispersion over long distance transmission.